CFD study of relation between ventilation velocity and smoke backlayering distance in large closed car parks

When fire occurs in a car park, smoke is often extracted by means of a horizontal ventilation system. To design this system, a necessary extraction velocity is needed, in order to guarantee a certain smoke clearance in the car park. In the present paper, a large number of car park CFD simulations are performed for use as ‘numerical experiments’. Four parameters are varied (convective heat release rate per unit area, fire source area, car park height and car park width). From the parameter variation, three formulae are proposed for the calculation of the required extraction velocity of hot smoke, corresponding to a certain smoke backlayering distance. These formulae are only valid for large closed car parks with flat ceiling and uni-directional smoke and ventilation flow pattern. Agreement with full-scale car park experiments confirms the expressions for the studied configuration.

► Large set of CFD simulations are used as ‘numerical experiments’.
► Critical inlet velocity in car parks depends on convective HRRPUA and fire source area.
► Formulae for outlet velocity and backlayering distance are also proposed.
► Agreement with full-scale car park experiments is shown.